Not Applicable
This invention relates to the field of methods and devices for the embolization of vascular aneurysms and similar vascular abnormalities. More specifically, the present invention relates to a mechanism for deploying an endovascular implant, such as a microcoil, into a targeted vascular site, and releasing or detaching the implant in the site.
The embolization of blood vessels is desired in a number of clinical situations. For example, vascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particularly intracranial aneurysms. In recent years, vascular embolization for the treatment of aneurysms has received much attention. Several different treatment modalities have been employed in the prior art. U.S. Pat. No. 4,819,637xe2x80x94Dormandy, Jr. et al., for example, describes a vascular embolization system that employs a detachable balloon delivered to the aneurysm site by an intravascular catheter. The balloon is carried into the aneurysm at the tip of the catheter, and it is inflated inside the aneurysm with a solidifying fluid (typically a polymerizable resin or gel) to occlude the aneurysm. The balloon is then detached from the catheter by gentle traction on the catheter. While the balloon-type embolization device can provide an effective occlusion of many types of aneurysms, it is difficult to retrieve or move after the solidifying fluid sets, and it is difficult to visualize unless it is filled with a contrast material. Furthermore, there are risks of balloon rupture during inflation and of premature detachment of the balloon from the catheter.
Another approach is the direct injection of a liquid polymer embolic agent into the vascular site to be occluded. One type of liquid polymer used in the direct injection technique is a rapidly polymerizing liquid, such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, that is delivered to the target site as a liquid, and then is polymerized in situ. Alternatively, a liquid polymer that is precipitated at the target site from a carrier solution has been used. An example of this type of embolic agent is a cellulose acetate polymer mixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO). Another type is ethylene vinyl alcohol dissolved in DMSO. On contact with blood, the DMSO diffuses out, and the polymer precipitates out and rapidly hardens into an embolic mass that conforms to the shape of the aneurysm. Other examples of materials used in this xe2x80x9cdirect injectionxe2x80x9d method are disclosed in the following U.S. Pat. Nos. 4,551,132xe2x80x94Pxc3xa1sztor et al.; 4,795,741xe2x80x94Leshchiner et al.; 5,525,334xe2x80x94Ito et al.; and 5,580,568xe2x80x94Greff et al.
The direct injection of liquid polymer embolic agents has proven difficult in practice. For example, migration of the polymeric material from the aneurysm and into the adjacent blood vessel has presented a problem. In addition, visualization of the embolization material requires that a contrasting agent be mixed with it, and selecting embolization materials and contrasting agents that are mutually compatible may result in performance compromises that are less than optimal. Furthermore, precise control of the deployment of the polymeric embolization material is difficult, leading to the risk of improper placement and/or premature solidification of the material. Moreover, once the embolization material is deployed and solidified, it is difficult to move or retrieve.
Another approach that has shown promise is the use of thrombogenic filaments, or filamentous embolic implants. One type of filamentous implant is the so-called xe2x80x9cmicrocoilxe2x80x9d. Microcoils may be made of a biocompatible metal alloy (typically platinum and tungsten) or a suitable polymer. If made of metal, the coil may be provided with Dacron fibers to increase thrombogenicity. The coil is deployed through a microcatheter to the vascular site. Examples of microcoils are disclosed in the following U.S. Pat. Nos. 4,994,069xe2x80x94Ritchart et al.; 5,133,731xe2x80x94Butler et al.; 5,226,911xe2x80x94Chee et al.; 5,312,415xe2x80x94Palermo; 5,382,259xe2x80x94Phelps et al.; 5,382,260xe2x80x94Dormandy, Jr. et al.; 5,476,472xe2x80x94Dormandy, Jr. et al.; 5,578,074xe2x80x94Mirigian; 5,582,619xe2x80x94Ken; 5,624,461xe2x80x94Mariant; 5,645,558xe2x80x94Horton; 5,658,308xe2x80x94Snyder; and 5,718,711xe2x80x94Berenstein et al.
The microcoil approach has met with some success in treating small aneurysms with narrow necks, but the coil must be tightly packed into the aneurysm to avoid shifting that can lead to recanalization. Microcoils have been less successful in the treatment of larger aneurysms, especially those with relatively wide necks. A disadvantage of microcoils is that they are not easily retrievable; if a coil migrates out of the aneurysm, a second procedure to retrieve it and move it back into place is necessary. Furthermore, complete packing of an aneurysm using microcoils can be difficult to achieve in practice.
A specific type of microcoil that has achieved a measure of success is the Guglielmi Detachable Coil (xe2x80x9cGDCxe2x80x9d). The GDC employs a platinum wire coil fixed to a stainless steel guidewire by a welded connection. After the coil is placed inside an aneurysm, an electrical current is applied to the guidewire, which oxidizes the weld connection, thereby detaching the coil from the guidewire. The application of the current also creates a positive electrical charge on the coil, which attracts negatively-charged blood cells, platelets, and fibrinogen, thereby increasing the thrombogenicity of the coil. Several coils of different diameters and lengths can be packed into an aneurysm until the aneurysm is completely filled. The coils thus create and hold a thrombus within the aneurysm, inhibiting its displacement and its fragmentation.
The advantages of the GDC procedure are the ability to withdraw and relocate the coil if it migrates from its desired location, and the enhanced ability to promote the formation of a stable thrombus within the aneurysm. Nevertheless, as in conventional microcoil techniques, the successful use of the GDC procedure has been substantially limited to small aneurysms with narrow necks.
A more recently developed type of filamentous embolic implant is disclosed in U.S. Pat. No. 6,015,424xe2x80x94Rosenbluth et al., assigned to the assignee of the present invention. This type of filamentous embolic implant is controllably transformable from a soft, compliant state to a rigid or semi-rigid state. Specifically, the transformable filamentous implant may include a polymer that is transformable by contact with vascular blood or with injected saline solution, or it may include a metal that is transformable by electrolytic corrosion. One end of the implant is releasably attached to the distal end of an elongate, hollow deployment wire that is insertable through a microcatheter to the target vascular site. The implant and the deployment wire are passed through the microcatheter until the distal end of the deployment wire is located within or adjacent to the target vascular site. At this point, the filamentous implant is detached from the wire. In this device, the distal end of the deployment wire terminates in a cup-like holder that frictionally engages the proximal end of the filamentous implant. To detach the filamentous implant, a fluid (e.g., saline solution) is flowed through the deployment wire and enters the cup-like holder through an opening, thereby pushing the filamentous implant out of the holder by fluid pressure.
While filamentous embolic implants have shown great promise, improvement has been sought in the mechanisms for deploying these devices. In particular, improvements have been sought in the coupling mechanisms by which the embolic implant is detachably attached to a deployment instrument for installation in a target vascular site. Examples of recent developments in this area are described in the following patent publications: U.S. Pat. Nos. 5,814,062xe2x80x94Sepetka et al.; 5,891,130xe2x80x94Palermo et al.; 6,063,100xe2x80x94Diaz et al.; 6,068,644xe2x80x94Lulu et al.; and EP 0 941 703 A1xe2x80x94Cordis Corporation.
There is still a need for further improvements in field of coupling mechanisms for detachably attaching an embolic implant to a deployment instrument. Specifically, there is still a need for a coupling mechanism that provides for a secure attachment of the embolic implant to a deployment instrument during the deployment process, while also allowing for the easy and reliable detachment of the embolic implant once it is properly situated with respect to the target site. It would also be advantageous for such a mechanism to allow improved control of the implant during deployment, and specifically to allow the implant to be easily repositioned before detachment. Furthermore, the coupling mechanism should be adaptable for use with a wide variety of endovascular implants, and it should not add appreciably to their costs.
Broadly, the present invention is a mechanism for the deployment of a filamentous endovascular device, such as an embolic implant, comprising an elongate, flexible, hollow deployment tube having an open proximal end, and a coupling element attached to the proximal end of the endovascular device. The deployment tube includes a distal section terminating in an open distal end, with a lumen defined between the proximal and distal ends. A retention sleeve is fixed around the distal section and includes a distal extension extending a short distance past the distal end of the deployment tube. The endovascular device is attached to the distal end of the deployment tube during the manufacturing process by fixing the retention sleeve around the coupling element, so that the coupling element is releasably held within the distal extension proximate the distal end of the deployment tube. In use, the deployment tube, with the implant attached to its distal end, is passed intravascularly through a microcatheter to a target vascular site until the endovascular device is fully deployed within the site. To detach the endovascular device from the deployment tube, a biocompatible liquid (such as saline solution) is injected through the lumen of the deployment tube so as to apply pressure to the upstream (interior) side of the coupling element. The coupling element is thus pushed out of the retention sleeve by the fluid pressure of the liquid, thereby detaching the endovascular device from the deployment tube.
The coupling element may be a solid xe2x80x9cplugxe2x80x9d of polymeric material or metal, or it may be formed of a hydrophilic polymer that softens and becomes somewhat lubricious when contacted by the injected liquid. With the latter type of material, the hydration of the hydrophilic material results in physical changes that reduce the adhesion between the coupling element and the sleeve, thereby facilitating the removal of the coupling element from the sleeve upon the application of liquid pressure. Alternatively, the coupling element can be made principally of a non-hydrophilic material (polymer or metal), coated with a hydrophilic coating.
In a specific preferred embodiment, the retention sleeve is made of polyethylene terephthalate (PET), and the coupling element is made of a hydrogel, such as a polyacrylamide/acrylic acid mixture. In another preferred embodiment, both the retention sleeve and the coupling element are made of a polyolefin. In still another preferred embodiment, the retention sleeve is formed of a fluoropolymer, and the coupling element is formed of a metal. Hydrophilic coatings, such as those disclosed in U.S. Pat. Nos. 5,001,009 and 5,331,027, may be applied to any of the non-hydrophilic coupling elements.
In an alternative embodiment, the retention sleeve is made of a shape memory metal, such as the nickel-titanium alloy known as nitinol. In this alternative embodiment, the coupling element would be made of one of the hydrophilic materials mentioned above, or it may be made of a non-hydrophilic material with a hydrophilic coating.
The deployment tube, in the preferred embodiment, comprises a main section having an open proximal end, a distal section terminating in an open distal end, and a transition section connected between the main and distal sections. A continuous fluid passage lumen is defined between the proximal and distal ends. The distal section is shorter and more flexible than the transition section, and the transition section is shorter and more flexible than the main section. This varying flexibility is achieved by making the main section as a continuous length of flexible, hollow tube, the transition section as a length of hollow, flexible laser-cut ribbon coil, and the distal section as a length of flexible, hollow, helical coil. The sections may be joined together by any suitable means, such as soldering.
Preferably, an air purge passage is provided either through or around the coupling element. The purge passage is dimensioned so that a low viscosity fluid, such as saline solution, is allowed to pass freely through it, but a relatively high viscosity fluid, such as a contrast agent, can pass through it only slowly. Before the deployment tube and the attached implant are introduced intravascularly to the target site, a saline solution is injected under low pressure through the lumen of the deployment tube to displace air from the lumen out through the purge passage. After the implant is located within the target site, a high viscosity contrast agent is injected into the deployment tube lumen to purge the remaining saline solution through the purge passage, but, because the contrast agent cannot pass quickly and freely through the purge passage, it builds up pressure on the proximal surface of the coupling element until the pressure is sufficient to push the coupling element out of the retention sleeve.
Any of the embodiments may employ an anti-airflow mechanism for preventing the inadvertent introduction of air into the vasculature during deployment of the implant. One such mechanism comprises an airtight, compliant membrane sealingly disposed over the distal end of the deployment tube. The membrane is expanded or distended distally in response to the injection of the liquid, thereby forcing the implant out of the retention sleeve.
Another such anti-airflow mechanism comprises an internal stylet disposed axially through the deployment tube. The stylet has a distal outlet opening adjacent the distal end of the deployment tube, and a proximal inlet opening in a fitting attached to the proximal end of the deployment tube. The fitting includes a gas/air venting port in fluid communication with the proximal end of the deployment tube. The gas venting port, in turn, includes a stop-cock valve. In use, the liquid is injected through the stylet with the stop-cock valve open. The injected liquid flows out of the stylet outlet opening and into the deployment tube, hydraulically pushing any entrapped air out of the venting port. When liquid begins flowing out of the venting port, indicating that any entrapped air has been fully purged from the deployment tube, the stop-cock is closed, allowing the continued flow of the liquid to push the implant out of the retention sleeve, as described above.
As will be appreciated more fully from the detailed description below, the present invention provides a secure attachment of the embolic implant to a deployment instrument during the deployment process, while also allowing for the easy and reliable detachment of the embolic implant once it is properly situated with respect to the target site. The present invention also provides improved control of the implant during deployment, and specifically it allows the implant to be easily repositioned before detachment. Furthermore, the present invention is readily adaptable for use with a wide variety of endovascular implants, without adding appreciably to their costs.